Due to concerns of insufficient petroleum raw material storage and supply, issues of rocketed petrochemical prices and insufficient petrochemical raw material sources are becoming worse, and in the production, use, and waste management of petrochemical products, large amounts of pollutants are produced, thus causing many environmental issues. Therefore, advanced nations of the world all list plant-based biomaterials as an important development project and an important key industrial raw material for replacing petrochemical raw materials in the future. In nature, the lignin reserves are only second to cellulose, and globally about 50 billion tons are produced each year. Lignin is abundant and cheap and has great business potential, and lignin has polyaromatic ring structure mechanical properties and good chemical resistance, and is therefore very suitable for the development of bio-composite materials. However, the application of internationally-developed biomaterials (such as lignin) in polymer composite materials is still very limited, mainly due to a large number of —OH functional groups and benzene ring structures of the lignin and strong intermolecular forces (such as hydrogen bonding) and π-π attraction force, such that lignin is not readily dispersed in a polymer substrate, and as a result a greater amount thereof causes worse mechanical properties. Only the uniform dispersion of lignin in a polymer substrate can effectively increase the mechanical properties of the bio-composite material and reduce the cost, and therefore the mixing and dispersion of lignin and the modification technique thereof have become one of the most important techniques to be established in domestic industry.
Currently, the development of lignin application in a polymer composite material is still very limited. If lignin is directly mixed with polyol for foaming, then since the dispersibility and the stability of lignin in polyurethane (PU) are poor, a greater amount thereof causes worse compressive strength. For the sulfonate lignin, after a lignin is modified via an ion exchange method, the lignin can be dissolved in polyol for foaming. However, modifying a lignin via an ion exchange method significantly increases the cost of the lignin. Therefore, the technique is greatly limited.